Generations may be non-stationary distributed since their nodes may belong to communities with different distributions and the graph is not necessarily fully connected, Fig.REF . A community
structure is 'the organization of vertices in clusters, with many edges joining
vertices of the same cluster and comparatively few edges joining vertices of different clusters' [1]}. There are methods to extract the community structure of large networks, see, for instance, [2]}, [3]}.
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